Should the game choose swimming in a liquid:
it is an excellent choice.

Check swimming in:
if the noun is a container:
if a random thing in the noun is not a liquid:
say "There's nothing in there to swim in and it would be too small anyway.";
otherwise:
say "It's too small to swim in.";
otherwise if the noun is not a liquid:
say "That's not liquid!";
otherwise:
say "There's not enough of it to go swimming in.";
stop the action.